1. Field of the Invention
The present invention relates to a projection display apparatus which projects an image displayed on a display panel onto a screen with magnification by using a projection lens and which is suitable for obtaining a large image.
2. Related Background Art
The demand for a display on a large screen has recently increased, and projection displays can be watched in many places today. FIG. 8 shows the composition of a conventional projection display apparatus used in such places. Referring to FIG. 8, the projection display apparatus comprises an illumination optical system 1, a display panel 2, such as a liquid crystal light valve, a projection lens 3 and a screen 4. A large screen display is performed by illuminating an image formed on the display panel 2 by the illumination system 1 and projecting the image with magnification onto the screen 4 through the projection lens 3.
However, the above conventional apparatus has a disadvantage: when a bundle of rays from the projection lens 3 are obliquely projected onto the screen 4, that is, when the optical axis of the projection lens 3 is not perpendicular to the screen 4, trapezium distortion is caused by the influence of the tilt in the projected image. In particular, since the relative relationship between the screen and the projection lens varies in accordance with the situation, in reality, the screen and the projection lens are likely to be arranged such that the trapezium distortion is extremely noticeable.
On the other hand, Japanese Laid-Open Patent Application No. 63-52585 discloses that an image is projected onto a screen by decentering the whole projection lens in parallel. However, since the whole projection lens is decentered, the diameter of the whole projection lens is required to be sufficiently long, and the decentering amount of the image with respect to that of the lens, that is, the sensitivity, is comparatively small.